1. FIELD OF THE INVENTION
The present invention relates to wind energy conversion systems, and more particularly to a control system for a wind machine that incorporates a laser Doppler anemometer to sense wind gusts.
2. DESCRIPTION OF THE PRIOR ART
It is well known to use a wind mill or wind machine for the conversion of wind energy to electrical energy. One known construction for such a wind machine includes a relatively large propeller having a shaft that is mechanically coupled to the shaft of an electric generator. Wind incident upon the propeller interacts aerodynamically with the propeller blades to impart forces thereon that rotate the propeller shaft and the generator shaft.
Generally the efficiency of a wind energy conversion machine is dependent upon the ratio of the speed of the wind to the tip speed of the propeller blade which is based on the radius of the blade and the angular rotation of the propeller. The rotational speed of the propeller is dependent upon both the wind speed and the magnitude of the electrical load powered by the generator.
As is also well-known an electrical load imparts a torque which counteracts the torque induced by the wind. Thus, the load torque of the generator tends to slow down the propeller rotation, while the wind torque tends to increase the rate of movement of the propeller. Consequently, the rate of rotation of the propeller can be varied for a given wind speed by altering the electrical load on the generator. Such control of the propeller rotation rate and accordingly the speed of the propeller blade tip permits adjustment of the tip speed ratio for improved efficiency of the wind energy conversion process.
A common problem arising in the use of wind machines is the unpredictable variations of wind speed that result in corresponding variations in the tip speed ratio. This problem is of particular concern in the case of wind gusts wherein the wind speed changes far more rapidly than the propeller can change its rotational speed. As a result, the efficiency of the wind energy conversion process usually decreases when there are variable wind speeds and is significantly affected by wind gusts.
One method of dealing with the problem of variable wind speed and wind gusts is to employ mechanical anemometers upwind of the wind machine to measure the wind intensity. Such measurements provide advance information about wind speed which can then be utilized to alter the electrical load on the generator so as to optimize the tip speed ratio.
However, it has been found that the wind receptor cups of mechanical anemometers have significant inertia which retards the transmission of the wind speed information. Such delay hampers the ability to accurately control the tip speed ratio.
A further drawback in the use of mechanical anemometers is that such anemometers measure wind speed only at the site of the anemometer. Since wind speed measurements can vary markedly from point to point, the wind speed data obtained by use of a single mechanical anemometer may be inadequate and may not properly describe the wind condition which will be experienced by the propeller of the wind machine. Thus a mechanical anemometer does not adequately provide the information needed to attain optimum control of the tip speed ratio.